Genetic Improvement Of Thousand Seed Weight Of A Core Elite Restorer 621R In Brassica Napus L.

Oilseed rape（Brassica napus L.）not only provides high quality vegetable edible oil for human but also protein for the livestock industry.To increase the seed yield by improving the genetic gain is the first important way in rapeseed breeding to meet the demand of the world for oil and feed.The thousand seed weight（TSW）genetic improvement is a major goal in breeding because it is one of the important components of yield in rapeseed.621R is an elite restorer of polima cytoplasmic male sterility in our germplasm pool which harbor high combining ability and excellent lodging resistance,but with small seed.In this study,we explore to construct a high-throughput speed breeding method combine with marker assisted backcrossing selection to introgress the elite alleles of TSW QTL into 621R to accomplish the seed weight genetic improvement.The main results are as follows:1.The construction of a high-throughput speed breeding method for rapeseed.First,we have constructed a growth chamber in which cold air is directed to circulate from the roof to the air flue and pass the plants,finally flowing back to the roof to achieve a uniform temperature distribution in the chamber.The light is supplied by light emitting diode（LED）board,in which the ratio of red,blue and green light is 6:2:2.The light intensity is over 900μmol m^-2 s^-1 at 10 cm below the LED bars.The chamber is programmed to run a 22 h/2 h（light/dark）photoperiod at 22℃all day with a humidity of 70%.Under this environment condition,a typical spring type variety Westar only takes around 65 d to accomplish one life cycle.By vernalization of the germinated seeds,the semi winter type rapeseed germplasm 616R,627R,Zhongshuang11（ZS11）and 621R could accomplish their life cycle with around 75,75,80 and 85 d,respectively.Besides,by adding 500μmol m^-2 s^-1 far-red light,the typical winter type canola variety Darmor-bzh could finished its life cycle with around 125 d.In the breeding process,a 96-well tray is developed to culture the seedling,and as a result,about 1000 seedlings could be hold in one square meter.More importantly,in the total growth area of 10.8 m²,675–1,350 adult plants can be planted with a density of 62.5–125 plants m^-2.2.The development of molecular marker linked to the TSW QTLs.The information of the TSW QTLs of q SWA03-1,q SWA03-2,q SWA03-3,q SWA7-1,q SWA8,q SWA09（hereinafter referred to as A3-1,A3-2,A3-3,A7-1,A8,A9）was obtained based on the publications.A total 36 polymorphism marker were developed base on the resequencing data of the donors ZS11,Zheyou 50（ZY50）and the recurrent parent 621R.3.The development of the near-isogenic lines with different TSW QTL combination.In the breeding process,speed breeding combines with marker assisted selection were conducted to develop the near-isogenic lines（the genetic improved lines）.A total 13 advance lines were obtained,which include 621R^A3-2,621R ^A3-3,621R ^A9,621R^A3-2/A3-3,621R^A3-1/A9,621R^A3-2/A9,621R^A3-3/A9,621R^A3-1/A7-1/A8,621R^A3-2/A3-3/A9,621RA3-1/A3-2/A3-3,621RA3-2/A3-3/A7-1/A9,621RA3-1/A7-1/A8/A3-2/A3-3,621RA3-1/A7-1/A8/A3-2/A3-3/A9,respectively.Genome recovery rate evaluation of these lines using resequencing data indicated that the genome shows 97.17%,98.27%,98.56%,97.34%,95.02%,95.57%,97.72%,96.69%,93.69%,94.07%,93.79%,93.88%,91.79%to 621R,respectively.4.The major agronomy traits performance of 13 the genetic improved lines under field conditions.Base on the phenotype data from Gansu（GS）,Wuhan（WH）,Jiangling（JL）,a computational model that the lines used as fixed factor,the block and the environment used as random factor was employed to evaluate the performance of the genetic improved lines.The results demonstrated that all the genetic improved lines show a significant higher TSW than the recurrent parent 621R（2.53 g）.Mainly,621R^A3-2 showed the minimal TSW of 2.80 g whereas 621R^A3-1/A9 exhibited the maximal TSW of 4.18 g.The TSW of 621R^A9 is 3.51g,which is higher than all the lines that do not contain the locus q SWA09.We then investigated the yield per plant（YP）of the genetic improved lines and 621R.Overall,only 621R^{A3-1/A3-2/A3-3}（12.8 g）exhibited significantly higher YP than that of 621R（10.5 g）,while the YP of 621R^A3-3（8.5 g）was significantly lower than that of the recurrent parent.The other genetic improved lines showed slightly higher or lower YP than that of 621R.No significant differences in seed yield were detected among the genetic improved lines and 621R（249.3 g）.6 genetic improved lines showed slightly higher seed yield than that of 621R,and the seed yield of 621R^A3-2/A3-3 increased 15.6%compared to that of the recurrent parent,while 621R^A3-3 only harbor 201.5 g seed yield.Besides,the correlation analysis among different traits revealed that the seed number per silique was significant negative correlated to the TSW,reaching-0.67,but no significant coefficient of association between TSW and YP or yield was observed,which was 0.04 or-0.07,respectively.5.The TSW and the yield performance of the hybrids between the genetic improved lines and two male sterile lines.621R and the genetic improved lines were used as restorers to cross with 616A and RG430A,respectively,for producing F₁hybrids.The same computational model was employed to evaluate the performance of the hybrids.The TSW,YP and yield of the check hybrid 616A/621R were 3.70 g,17.2 g and 416.5 g,respectively.There are eight hybrids of the‘616A/genetic improved line’exhibited higher TSW than that of the check hybrid,while the remaining hybrids showed similar performance to the check hybrid.The hybrid 616A/621R^{A3-2/A3-3//A7-1A9}displayed the highest TSW（4.49 g）,whereas the TSW of the hybrid 616A/621R^A3-2 was the minimum one（3.58 g）.There was no significant difference of YP and seed yield between‘616A/genetic improved line’hybrids and the check hybrid.The coefficient of association of YP and yield to the TSW was 0.02 and-0.37,respectively,and showed no significant difference.The TSW,YP and yield of the hybrid RG430A/621R were3.98 g,19.0 g and 450.0 g,respectively,and ten hybrids of the‘RG430A/genetic improved line’exhibited higher TSW than that of RG430A/621R.The TSW of the hybrid RG430A/621R^{A3-1/A7-1/A8/A3-2/A3-3/A9} was 4.76 g,which is higher than that of all hybrids,while its YP and seed yield decreased 14%and 9.5%,respectively.The TSW of the hybrid RG430A/621R^A3-1/A9（4.51 g）was higher than that of the check hybrid RG430A/621R,and its seed yield increased 13%compaired to that of the check hybrid.The coefficient of association of YP and yield to the TSW was 0.12 and 0.20,respectively,and showed no significant difference.Summary,using speed breeding and marker assisted selection help to accelerate the introgression of the TSW QTL elite alleles into 621R,which leading to the significantly increase of TSW in 621R.Compared with the check hybrid,part of the genetic improved lines’hybrids showed high seed yield potentials.